Antireflection coatings for metasurfaces

Abstract

Antireflection coatings for metasurfaces are described herein. In some embodiments, the metasurface may include a substrate, a plurality of nanostructures thereon, and an antireflection coating disposed over the nanostructures. The antireflection coating may be a transparent polymer, for example a photoresist layer, and may have a refractive index lower than the refractive index of the nanostructures and higher than the refractive index of the overlying medium (e.g., air). Advantageously, the antireflection coatings may reduce or eliminate ghost images in an augmented reality display in which the metasurface is incorporated.

What is claimed is: 
     
         1 . An optical system comprising:
 an optical element comprising a metasurface that includes a plurality of nanostructures forming repeating unit cells, wherein, as seen in a top-down view, each unit cell comprises:
 a plurality of spaced-apart first nanostructures, each of the first nanostructures comprising:
 a first length; and 
 a first width, 
 wherein the first length is longer than the first width, 
 wherein the first length extends in a first direction and the first width extends in a second direction, 
 wherein the second direction crosses the first direction, 
 wherein the first widths of different ones of the plurality of spaced-apart first nanostructures differ from one another, wherein the first nanostructures are separated from each other by a gap along the first lengths of the first nanostructures; and 
 
 a plurality of spaced-apart second nanostructures disposed at a side of the plurality of spaced-apart first nanostructures, each of the second nanostructures comprising: having
 a second length extending in the second direction; and 
 a second width extending in the first direction, 
 wherein the second widths of different ones of the plurality of spaced-apart second nanostructures differ from one another, and 
 wherein the second nanostructures are separated from each other by a gap along the second lengths of the second nanostructures, 
 
 wherein the second direction crosses the first direction; and 
   an antireflection coating for the optical element comprising the metasurface, the antireflection coating comprising:
 a layer of an optically transparent material having a refractive index greater than 1 and less than a refractive index of a material comprising the metasurface, 
 wherein the layer of the optically transparent material is conformally disposed over the nanostructures of the metasurface to follow contours of the nanostructures without completely filling volumes separating each of the nanostructures such that a top surface of the optical element is non-planar, and wherein the unfilled volumes that separate the first nanostructures from the second nanostructures are of a different volume from the unfilled volumes that separate the first nanostructures or that separate the second nanostructures. 
   
     
     
         2 . The optical system of  claim 1 , wherein the optically transparent material comprises a polymer. 
     
     
         3 . The optical system of  claim 1 , wherein the optically transparent material comprises photoresist. 
     
     
         4 . The optical system of  claim 1 , wherein the optically transparent material has a refractive index from about 1.2 to about 2. 
     
     
         5 . The optical system of  claim 1 , wherein a distance from a topmost surface of the metasurface to a topmost surface of the antireflection coating is from about 10 nm to about 1 micron. 
     
     
         6 . The optical system of  claim 1 , wherein the antireflection coating reduces an amount of incident light reflected by the metasurface by more than about 50% as compared to an amount of incident light reflected by a substantially similar metasurface that does not include the antireflection coating. 
     
     
         7 . The optical system of  claim 6 , wherein the incident light has an incident angle from about −20° to 20°. 
     
     
         8 . The optical system of  claim 1 , wherein the antireflection coating has a thickness configured to provide destructive interference between light reflecting off a top surface of the antireflection coating and light reflecting off a bottom surface of the antireflection coating. 
     
     
         9 . The optical system of  claim 1 , wherein the metasurface comprises a diffraction grating. 
     
     
         10 . The optical system of  claim 1 , wherein the metasurface comprises an asymmetric diffraction grating. 
     
     
         11 . The optical system of  claim 1 , wherein the metasurface comprises a Pancharatnam-Berry phase optical element (PBOE). 
     
     
         12 . The optical system of  claim 1 , wherein the metasurface comprises multi-tier nanostructures. 
     
     
         13 . The optical system of  claim 1 , further comprising a waveguide, wherein the optical element is formed on or in the waveguide. 
     
     
         14 . The optical system of  claim 13 , wherein the optical element is an incoupling optical element. 
     
     
         15 . The optical system of  claim 13 , wherein the waveguide comprises an optically transmissive substrate, and wherein the metasurface overlies the substrate.